Sour gas often contains significant quantities of dissolved elemental sulfur, which tends to precipitate in numerous points during transport, including the well string, the gas gathering system, and in downstream gas treating and gas processing equipment. To avoid such problems, hydrocarbon oils can be injected into the well string or gathering system to solubilize the sulfur in the hydrocarbon liquid phase and to thereby prevent precipitation of the elemental sulfur. Most commonly, aromatic solvents (e.g., alkyl naphthalene) are used as solvents as they typically exhibit a higher sulfur solubility than paraffinic or naphthenic hydrocarbons. A typical example for such a system is described in U.S. Pat. No. 4,322,307.
Regeneration of sulfur laden aromatic hydrocarbon solvents is commonly achieved by contacting the rich solvent with an aqueous solution comprising an amine (e.g., ethylamine). In such systems, the sulfur is converted to a polysulfide and migrates into the aqueous phase, thereby regenerating the hydrocarbon solvent, which is then recycled. The aqueous solution containing the amine and polysulfide/sulfur is then regenerated by distillation to provide an aqueous amine solution as the overhead product and impure, molten elemental sulfur as the bottoms product. For example, U.S. Pat. No. 5,242,672 describes a typical regenerator unit. While such systems generally achieve desirable sulfur reduction in the sour gas, numerous difficulties nevertheless remain. Among other things, regeneration of the solvent using an amine solution requires significant quantities of energy for heating and pumping. Moreover, and depending on the particular sour gas, chemical stability of the amine solution may be less than desirable and require stabilizers and/or replacement of the amine. Also, the polysulfide and/or sulfur obtained from such regeneration may at least in some cases require additional processing to provide a desirable end product.
Alternatively, a dialkyldisulfide can be employed as a sulfur solvent as described, for example, in U.S. Pat. No. 3,531,160. In such systems, the dissolved sulfur is removed via distillation and/or by precipitation with a solvent (e.g., ketones or hydrocarbons) to regenerate the solvent. For high-temperature and high-pressure wells, the alkylsulfide or dialkyldisulfide may be amine activated as described in U.S. Pat. Nos. 4,248,817 or 4,290,900. Regeneration of the solvent is often achieved by precipitation of the dissolved sulfur. Such systems provide some advantages over paraffinic or naphthenic hydrocarbon-based sulfur dissolution systems, however, suffer from other disadvantages. For example, regeneration of the solvents is not always quantitative and, where activated, the solvents may degenerate and lose performance over time, especially under relatively harsh conditions of deep-well gas production. Thus, new solvent must typically be added to maintain desired performance. Further, regeneration in at least some of such systems still requires substantial quantities of energy.
Therefore, while numerous methods of sulfur solvent systems are known in the art, all or almost all of them suffer from one or more disadvantages. Consequently, there is still a need to provide improved systems and methods for sulfur solvent systems.